This invention relates broadly to a fastening device adapted to be secured adhesively to a primary work surface.
The invention more particularly relates to an adhesive fastening device designed to be secured and activated through the use of a U-shaped induction core.
The use of a U-shaped core with an exciter coil wound about a portion of the core to activate adhesive carrying devices is a highly efficient system. The legs of the core preferably abut the upper surface of an adhesive carrying device so that the device completes a magnetic flux circuit between the legs of the core thereby creating heat in the device by eddy currents and a hysteresis effect. The heat created in the device is conducted to the adhesive layer to raise it to its activating temperature and thus secure the device to a primary work surface. Since the flux density created in the fastener device is a critical parameter in achieving efficient heating, the device and the end faces of the core must be properly and carefully aligned to maximize the flux density and, of course, minimize the heat losses in the system. A proper bond also requires a sufficient amount of pressure applied to the device to insure that a proper wetting action exists between the faying surfaces of the device and the work surface. It, therefore, becomes advantageous to use the U-shaped core as a pressure applying instrument as well as a heat generating instrument. Since the maximum utilization of adhesive and metal in an adhesive fastening device requires that the adhesive layer be closely adjacent to the margins of the device, the application of force on the device by the core during heating could cause adhesive to be forced outwardly toward the periphery of the device and into engagement with the end faces of the core. Such adhesive deposits on the core will harmfully affect subsequent similar applications because the end faces will not be capable of maintaining the close, critical spacing between the device to be heated and the end face. Such a spacing is directly related to the flux density and the heat created in the device and should be critically controlled.
It is, therefore, an object of the invention to provide an adhesive fastening device with structure that will permit a U-shaped core to apply pressure to the device during the heating thereof without harming the end surface of the core.
Still another object of the invention is to provide an adhesive fastening device with a means to accurately align the device with the end faces of an associated U-shaped core.
The above and other objects and advantages of the invention are fulfilled by an adhesive fastening device basically comprising a flat base having a pair of side marginal edges upturned so as to form parallel flanges. The flanges will extend a short distance perpendicularly to the base and preferably a distance not substantially greater than the thickness of the base. A secondary attachment means is, preferably integrally, formed on the base. This secondary means may take the form of an upstanding threaded stud, to permit subsequent fastening of a secondary workpiece to the fastening device after the adhesive fastener has been secured to the primary work surface. The upstanding flanges serve two important purposes in an attachment system utilizing a U-shaped core. Firstly, they provide means to carefully and predicably orient the device with the end surfaces of a core. This is accomplished, in a preferred embodiment, with an orienting structure having slots designed to register with the flanges and which are fixedly secured to the core so that the upturned edges are aligned with and abut the end surfaces of the core. Secondly, the edges provide a slight spacing between the adhesive layer and the region of abutting contact between the core and the device to minimize the probability that adhesive will flow outwardly from the perimeter of the device and into contact with end faces.
Other objects and advantages of this invention will become apparent upon reading the following detailed description and upon reference to the drawings.